Wireless communication using electromagnetic radiation e.g. radio and TV broadcasts needs a certain band of the available frequency spectrum. Using these bands is regulated by national and international bodies which assign frequency bands for specific uses, and in many cases license the rights to these. This frequency allocation process creates a band plan, which for technical reasons may assign unused spectrum between used transmission bands or channels to avoid interference. In this case, while the frequencies are unused, they have been specifically assigned for a purpose, such as a guard band. These unused spectrum may exist naturally between used channels, as assigning nearby transmissions to immediately-adjacent channels may cause disturbing interference to both.
As well as these technical assignment, there is also unused radio spectrum which has either not been in use, or is becoming free as a result of technical changes. In particular, the planned switchover to digital television may free up large areas within certain frequency range. This is because digital transmissions can be packed into adjacent channels, while analog ones cannot. This means that the band can be “compressed” into fewer channels, while still allowing for more transmissions.
In the United States, the Federal Communications Commission (FCC) has issued a ruling to allow devices that satisfy some conditions/requirements to be able to access the TV bands, which are un-used at a specific place and at a specific time. This part of TV spectrum is called White Space (WS). A device intended to use these available channels is a white-space device (WSD). These devices may be designed to detect the presence of existing signals, such as TV stations and other wireless users, and to then avoid the use of these channels. Early ideas proposed including GPS receivers and programming each white space device with a white space database (WS DB) of all TV stations in an area, however this would not have avoided other non-stationary or unlicensed users in the area, or any stations licensed or altered after the device was made.
A white space device generally needs to have the following capabilities: it is aware of or capable to determine its location (geographical location); it has access to a white space database, which contains the latest spectrum usage information with respect to places; it is able to detect occupation of the bands within the white space frequency spectrum (Sensing), etc.
Usually a white space device may need to possess the latest information of the white space database relevant to its location and transmits at proper frequency bands according to the latest white space database information. There may be multiple white space databases and each of them may contain the spectrum usage information for several areas.